Such a method is known from DE-U-9,115,389. In this known method the organic filtration material is deposited directly on to the grating floor. The result of this is that the filtration material will dry out and therefore be less active when the air to be cleaned is passed through it. The portions of the filtration material will also not adjoin well, so that at least part of the air shall be filtered less well.
The invention has the purpose of removing this disadvantage, and to that end, it provides that the grating floor is first provided with a layer of gravel, followed by the organic filtration material, and that during use the gravel is kept humid by spraying water on to it from nozzles provided close above the layer of gravel.
The thickness of the layer of gravel shall, for example, be approximately 20 mm.
To further counteract the drying-out of the filtration material, humidification of the filtration material can be provided and can occur at several levels, one level lies above the filtration material, and the other is located at about half the height of the filtration material, from which level the gravel is humidified as well.
Further, there is the possibility of pre-heating the air to be cleaned by passing it through tubing which is located either immediately above or also inside the filtration material itself. In this the heat released during the bio-activity in the filtration material is utilized.
Such a method offers advantages in particular in the cleaning of air with a relatively low termperature by which the bacterial activity of the filtration material could be adversely affected. Air with a relatively low temperature is present in, for example, water-purification installations.
The invention also relates to an apparatus for the application of the method described above, which apparatus is characterized in that substantially horizontally extending tubes, provided with nozzles, have been provided in the chamber, which pass through at least one vertical wall of the chamber to the exterior for the connection or supply lines of spraying water to it.
In order to pass the air to be cleaned in succession through two or more chambers, the apparatus according to the invention can be characterized in that some similarly embodied chambers can be stacked for cleaning the air in stages because the bottom edge of a chamber can not only be placed on top of the air supply room, but also on top of the top edge of a similar chamber, and that a roofing assembly, provided with means for lifting it and for the discharge of air from the chamber, can be placed on top of the top edge.
The passing of air to be cleaned through two or more chambers can be of importance when there are certain components in the air which must be removed by special bacteria while other bacteria, necessary for the cleaning of the air, could be killed by these components.
The dimensions of the length and the breadth of the chamber and the means for engaging it shall correspond substantially to those of a standard container. Owing to this a vehicle suitable for the transportation of containers can be used for the transportation of the filtration chambers. Then the removal of the filtration material from the chambers and the filling of these again with fresh filtration material can take place at a central location. Skilled personnel can be available at the central location for optimum filling of the chambers. Owing to this, a large share of the filtration material removed from a container can also be used again.
According to the invention a grating floor provided in a chamber shall in particular be formed by a number of bars, rods or the like which are either directly or indirectly connected to the walls of the chamber for forming a coarse grating, on top of which coarse grating a grating mat, consisting of cross-laid and interconnected plastic wires, is placed. Such a mat is commercially available, and a suitable spacing between the wires is e.g. approximately 7 mm.
DE-U-8,801,502 illustrates a bio filter in which a number of chambers too have been stacked. The organic filtration material lies directly on top of the grating in here too. In this the edges of the chambers must adjoin well, for which the corners of the chambers have been provided with tubes that will telescope when the chambers are stacked. Therefore, the chambers will only be able to have limited dimensions since assembly or disassembly will be difficult or impossible as a result of even small temperature differences of the chambers.
Further NL-A-8,303,031 illustrates a filtration apparatus which is particularly suitable for flue gases and in which the gas is first passed through a pre-treatment chamber in which a gravel bed is located, on top of which liquid is sprayed, and subsequently passed through a filtration unit consisting of a grating floor on which the biologically active material is located. Thus, the apparatus is complicated and the replacing of the exhausted material will be much more difficult to perform.